This invention relates to a hydraulic seal arrangement between two, more particularly co-rotating shafts of especially a gas turbine engine, where the radially outer shaft when viewed with reference to the shafts"" axis of rotation has an annulus extending radially outward along its circumference into which the radially inner shaft when viewed with reference to the shafts"" axis of rotation projects with a web that extends radially outward across its circumference, and which annulus can through an inlet area be filled siphon-fashion under centrifugal effect with a hydraulic medium at least in the area of the free end of the web when the shaft(s) is (are) rotating. For technically associated patents, reference is made to DE 33 28 057 A1.
Hydraulic seals between two rotating shafts where a hydraulic medium is introduced under centrifugal force between a web of an inner shaft and an annulus of an outer shaft, also called xe2x80x9ccentrifugal-force siphonsxe2x80x9d, have long been known as noncontacting, nonleaking seals. They are especially suitable for sealing shafts in relative motion one to the other. For this purpose, a hydraulic medium, more particularly oil from the oil circuit of the machine, more particularly a gas turbine engine containing the shafts, is ducted into said annulus where it forms a barrier under the centrifugal force produced by the rotation of the shaft(s).
No problems are encountered when such a simple, but very effective hydraulic seal is used in a relatively cool environment. But when such a seal according to the generic part of claim 1 is used in a relatively hot environment, where the shaft material in the region of said annulus may heat to around 500xc2x0 C., also the hydraulic medium (oil) would heat to this temperature and sooner or later inevitably begin to carbonize (coke). The resulting, at least partial hardening of the hydraulic medium and the associated adherence of coked oil on the walls confining the annulus or siphon obviously no longer ensure reliable sealing action.
In a broad aspect of the present invention, means is provided with which a hydraulic seal between two rotating shafts where a hydraulic medium is introduced under centrifugal force between a web of an inner shaft and an annulus of an outer shaft can be used also in a relatively hot environment.
It is a particular object of the present invention to provide an arrangement in which a means, branching off from an annulus area essentially farthest away from the inlet area, is provided for exhausting part of the hydraulic medium. In a preferred aspect, the inlet area of the annulus is provided at a point lying as far inside as possible, viewed radially, whereas the annulus area containing the exhaust means for the hydraulic medium is situated as far outside as possible, viewed radially, and close to that side of the annulus that lies opposite the inlet area. Further advantageous aspects of the present invention will become apparent from the following description.
In accordance with the present invention, continuous flow of hydraulic medium through the annulus forming the siphon is ensured when at least part of the hydraulic medium in the annulus is continuously exhausted and, naturally, replaced, or refilled, which requires that the annulus / siphon can essentially continuously be filled with hydraulic medium. As a result, fresh and hence relatively cold oil or hydraulic medium continuously enters the annulus/siphon, while hydraulic medium already heated by the environment is (partially, but preferably fully) exhausted from it. Accordingly, oil or hydraulic medium will not stay long enough in the annulus to carbonize. Simultaneously, the continuous flow of hydraulic medium through the annulus causes sufficient heat to be dissipated from the containing walls of the annulus to cool them, so that, again, the risk of coking is eliminated. Locating the means to exhaust at least some of the hydraulic medium in an area that is essentially farthest away from the inlet area makes sure that the hydraulic medium in the annulus is at least cooled as best as possible, if not even fully replaced, by the continuous inflow of hydraulic medium.
Design options to bleed off some of the hydraulic medium from the annulus or siphon may take several different forms. Two preferred embodiments are shown in respective partial sectional views in the accompanying FIGS. 1 and 2 and are described more fully below. On the drawings, the reference numerals refer to the same components respectively.